1. Field of the Invention
The present invention relates to an image signal processing apparatus for processing an image signal.
2. Description of the Related Art
Electronic still video cameras arranged to record a still image signal on a video floppy disc which is a magnetic disc have heretofore been known as one type of apparatus for processing an image signal.
Some of the electronic still video cameras include memory devices, and are arranged to temporarily store in the memory device a still image signal supplied from a video camera part or external equipment such as a still video reproducing apparatus and read out the still video signal stored in the memory device to record it on a video floppy disc as well as to output it to external equipment such as a monitor.
Such an electronic still video camera including memory devices is arranged to separate a still image signal supplied from the video camera part or the external equipment such as a still video reproducing apparatus into two signal components: a luminance signal and color-difference signals, input the two signal components as analog signals, convert the analog signals into digital signals, respectively, and write the respective digital signals into the separate memory devices. If the digital signals written into the respective memory devices are to be supplied to external equipment such as a monitor, the color-difference signals of digital form are converted into a digital chrominance signal by balanced modulation before the digital signals outputted from the respective memory devices are subjected to D/A conversion. Then, the digital chrominance signal is subjected to D/A conversion and the obtained analog signal is frequency-multiplexed onto the D/A-converted luminance signal, thereby forming a composite color still image signal. The composite color still image signal is supplied to the desired external equipment. If the two signal components written into the memory devices are to be recorded on a video floppy disc, the luminance signal and the color-difference signals written into the respective memory devices are respectively converted from digital to analog, and the respective analog signals are frequency-modulated. The frequency-modulated luminance signal and the frequency-modulated color-difference signals are frequency-multiplexed to form a recording signal, and the recording signal is recorded on the video floppy disc.
However, such a conventional electronic still video camera has a number of disadvantages. For example, since the digital color-difference signals and the digital chrominance signal are separately formed, separate D/A converters are needed to perform D/A conversion of the respective signals. Since a D/A converter for D/A conversion of the digital luminance signal is also needed, a total of three D/A converters must be incorporated.
As can be seen from the above description, the conventional electronic still video camera needs a complicated arrangement and it has been difficult to reduce the size, weight and cost of the apparatus.